mid-14c., from Old French blasfemer "to blaspheme" (14c., Modern French blasphémer), from Church Latin blasphemare (also in Late Latin "revile, reproach"), from Greek blasphemein "to speak lightly or amiss of sacred things, to slander," from blasphemos "evil-speaking" (see blasphemy). A reintroduction after the original word had been worn down and sense-shifted to blame. Related: Blasphemed; blaspheming.